RFR: 8360025: (se) Convert kqueue Selector Implementation to use FFM APIs

[Darragh Clarke]

On Tue, 14 Oct 2025 10:53:51 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR was originally part of #25546, though that PR has been split in 2, the first chunk was https://github.com/openjdk/jdk/pull/27590.
>> 
>> This PR aims to convert KQueue to use FFM apis, the first PR in this area added all the jextract generated code needed, while this PR modifies some of the jextract code and then uses it with Kqueue.
>> 
>> A brief rundown of the changes:
>> - The files `errno_h$shared.java` , `kqueue_h$shared.java`, `timespec_h$shared.java` and `timespec_h.java` have all been deleted. This is because they all contained shared elements that could be moved into the Utility file `FFMUtils.java`
>> - `Kqueue.c` has been deleted, and all native methods in the other `KQueue` files have been replaced with references to the generated files kevent and kqueue. This is the bulk of the changes
>> - Both the `Kqueue()` and `Kevent()` methods in `kqueue_h.java`  were modified to use adapted method handles that will return the errno value
>
> src/java.base/macosx/classes/jdk/internal/ffi/generated/kqueue/kqueue_h.java line 45:
> 
>> 43:     }
>> 44: 
>> 45:     static final SymbolLookup SYMBOL_LOOKUP = SymbolLookup.loaderLookup()
> 
> Can we remove this static field?

You're right, i'll remove it

> src/java.base/macosx/classes/jdk/internal/ffi/generated/kqueue/kqueue_h.java line 152:
> 
>> 150: 
>> 151:         public static final MemorySegment ADDR = FFMUtils.findOrThrow("kevent");
>> 152:         public static final MethodHandle HANDLE = Linker.nativeLinker().downcallHandle(ADDR, DESC,
> 
> I would suspect we do not use `ADDR` and `HANDLE` so maybe we do not have to store them?

The only place that uses them is `ADAPTED` directly below them, so it could get moved into that instead of being stored, though it might be a slight hit to readability.

edit: I see theres also getters for them, though I don't think those are used anywhere

> src/java.base/macosx/classes/jdk/internal/ffi/util/FFMUtils.java line 39:
> 
>> 37: public final class FFMUtils {
>> 38: 
>> 39:     public static final ValueLayout.OfBoolean C_BOOL =
> 
> This class is specific for macOS but yet, it appears it would work for any platform (given its use of canonical layouts)?

Yeah I think with minimal changes (maybe none?) this could be moved to shared, though I don't know if we want to keep this current PR as minimal in scope as possible. I played it safe with just putting it in Mac for now but I'm happy for it to move

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PR Review Comment: https://git.openjdk.org/jdk/pull/27796#discussion_r2429140759
PR Review Comment: https://git.openjdk.org/jdk/pull/27796#discussion_r2429142232
PR Review Comment: https://git.openjdk.org/jdk/pull/27796#discussion_r2429157101